Is there a name for the logical fallacy of assuming that B is true because A is true and B often results from A. I'm not sure if I'm phrasing that correctly. Here is the statement:

She worked at Big Name Company; she must be good.

It's not quite "cum hoc ergo propter hoc" or "post hoc ergo propter hoc", because both of those assume that B is true.

In this case:

A is true (she did work there)
B often results from A (the company has high standards and people who have worked there are usually good)
But B is not necessarily true (in this case, it wasn't.)

Is there a name for that?

  • She did work there, but doesn't anymore - what does that say about her?
    – gnasher729
    Commented Jan 31, 2017 at 18:47

2 Answers 2


its a simple enthymeme, a syllogism with an unstated premise. the missing premise is sth like "anybody who works for Big Name Company is good". She worked there; therefore she's good. (drop "must be").

  • (Yes, thank you -- the "must be" was my way of characterizing the speaker's attitude, a verbal shrug.) The difference in this example is that the missing premise might be incorrect. Socrates is mortal because he is human and yes, in fact, all humans are mortal. Big Name usually produces good people... but sometimes not. is there a name for an enthymeme in which the missing premise is false, or at least not necessarily true? Or does "enthymeme" refer to the structure of the missing premise, whether true or not?
    – Ohthatdeb
    Commented Jan 20, 2017 at 1:41
  • I disagree. The premise is clearly stated - it's just insufficient.
    – Canyon
    Commented Jan 20, 2017 at 3:12
  • @Ohthatdeb: I'm not sure. I think the idea is just ustated premises, w/o regard to their truth values, but I could be wrong.
    – user20153
    Commented Jan 20, 2017 at 16:19

This is inductive reasoning. It's an argument that carries with it no necessity, only tendencies.

If you're interested in more details, check out Hume. Essentially his argument is that the only reason we think things in the future are going to be like things in the past is that in past futures, things have always resembled past pasts. Clearly that's not enough to show necessity. It's a really very interesting problem, and the one that woke Kant out of his "dogmatic slumber", and so definitely worth pursuing.

The modern response to it that I'm most familiar with is Bayesian Epistemology - essentially just statistics. It's Bayesian in particular because it follow's Bayes' rule for adjusting one's degree of belief based on new evidence, and how unexpected that evidence is. Whether or not it is in fact epistemology in the traditional sense is up for debate, but it's certainly a useful way to view many facts in the material world.

  • Thank you -- I'll admit that my philosophical chops are a bit rusty, so I'll need to take some time with this! Here's the context -- I am editing a book on decision making. This scenario is given as an example of the "auto pilot" thinking we do every day, without which we would all still be thinking through our breakfast options. I'm looking for terminology to describe the unrecognized logical fallacies that lead us to make poor decisions. Hiring a consultant because your autopilot says "Ooh! Big Name. She's good" is an example of _____ (??) That sort of thing.
    – Ohthatdeb
    Commented Jan 20, 2017 at 1:53

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